S-Shaped composition dependence of excess thermodynamic quantities for cyclohexane mixtures with globular alkanes

Expansion coefficients , isothermal compressibilities, thermal pressure coefficients and heat capacities have been measured at 25°C for the cyclohexane+trans-decalin system. An S-shaped composition dependence, positivelnegative for highllow cyclohexane compositions is found for C _p ^E dV ^E /dT and the thermal expansion contribution to C _p ^E namely VT. The thermal motion contribution to C _p ^E , namely C _v is close to zero. The positive excursion of these mixing quantities at high cyclohexane content is anomalous. Correspondingly, the mixing quantity-VT deviates strongly in this region from the predicted equality with H ^E . The literature and this work show that all these excess quantities behave similarly for cyclohexane mixed with cyclooctane, methylcyclohexane and some highly branched alkanes. The unusual composition dependence of the thermodynamic quantities is consistent with order occurring when any large alkane molecule of globular shape is added to cyclohexane. This is speculatively associated with an interference by the globular alkane with the relatively free rotation of cyclohexane molecules.     

Determination of unreacted 2,4-toluene diisocyanate (2,4TDI) and 2,6-toluene diisocyanate (2,6TDI) in foams at ultratrace level by using HPLC-CIS-MS-MS

Isocyanates can cause occupational asthma. By using available HPLC-UVF methods, isocyanates can be quantified only at levels above 1% of the Permissible Exposure Limits (PEL). Once sensitized, workers can react to concentrations below these limits of detection (LOD) making these methods insufficiently sensitive to adequately evaluate trace amounts of isocyanates present in air or in materials at safe levels for sensitized workers. This article describes a novel method for isocyanate analysis allowing the quantification of 2,4TDI and 2,6TDI monomers at very low concentrations using HPLC-CIS-MS-MS. The method's sensitivity increases with a decrease in the alkali radius. The LOD is 0.039 ng mL(-1) for 2,4TDI and 0.100 ng mL(-1) for 2,6TDI in solution when lithium is the alkali adduct, which is 20 times more sensitive than HPLC-UVF method. This new method allows determination in foam at levels of 0.078 ng g(-1) for 2,4TDI and 0.200 ng g(-1) for 2,6TDI respectively, for a 0.5 g foam sample. This is more than 100 times more sensitive than other methods for determining free monomers in solid materials. Analytical reproducibility and precision are better than 92% and 93% for both diisocyanate monomers. The use of HPLC-UVF conventional method failed to detect unreacted isocyanates in foam samples, but TDI monomers were quantified by HPLC-CIS-MS-MS.     

Organometallic derivatives of N-phenylmaleimidetriazoles and quinonetriazoles

The syntheses, properties, and structures of Mn, Cr, Re, and W organometallic derivatives of N-phenyl-1,2,3-triazoles and quinone-1,2,3-triazoles are described. The X-ray structures of eleven compounds are described. 9, a = 11.588(2), b = 11.904(2), 14.179(2) Å, α = 69.407(3)°, β = 70.879(3)°, γ = 78.627(3)°, P-1, R = 0.0739. 10, a = 7.643(1), 9.375(1), 13.077(2) Å, α = 74.292(2)°, β = 74.763(2)°, γ = 71.694(2)°. P-1, R = 0.0415. 11, a = 14.325(4) Å, b = 17.508(5) Å, c = 15.465(5), β = 99.282(5)°, P2/n, R = 0.0610. 17, a = 7.679(2) Å, b = 9.273(2) Å, c = 13.084(3) Å, α = 75.166(3)°, β = 74.651(3)°, γ = 71.613(3)°, P-1, R = 0.0428. 18, a = 5.757(1), 13.470(3), 23.056(4) Å, P2₁2₁2₁, R = 0.0697. 19, a = 8.118(1) Å, b = 10.471(2), 15.027(2) Å, α = 72.848(2)°, β = 82.237(2)°, γ = 71.829(2)°, P-1, R = 0.0597. 23, a = 7.993(1), 9.302(1) Å. C = 13.318(2) Å, α = 94.471(2)°, β = 105.269(2)°, γ = 109.523(2)°, P-1, R = 0.0271. 24, a = 7.583(4), 9.595(5), 13.030(6) Å, α = 76.389(7)°, β = 74.883(7)°, γ = 71.102(7)°, P-1, R = 0.0502. 26, a = 32.757(5) Å, b = 6.7083(9) Å, c = 26.033(4) Å, β = 128.895(5)°, C2/c, R = 0.0489. 31, a = 8.302(2), 8.347(2), 13.794(4) Å, α = 85.749(4)°, β = 81.176(4)°, γ = 74.849(4)°, P-1, R = 0.0400. 32, a = 11.321(2) Å, b = 12.110(2), 18.179(3) Å, β = 103.951(3)°, P2₁/c, R = 0.0318.     

Use of headspace solid-phase microextraction for the quantification of poly(3-hydroxybutyrate) in microbial cells

Biopolymers such as poly(hydroxyalkanoates) (PHAs) have received much attention due to their physico-chemical properties, biodegradability, and biocompatibility that make them good candidates for industrial and medical applications. Produced by some microorganisms PHAs accumulate within the cells of these organisms. The optimization of microbial processes to produce PHAs at a lower cost requires rapid and accurate techniques for quantification of the biopolymer in biomass. The present study describes a method based on solid-phase microextraction (SPME) coupled to gas chromatography (GC) for the determination of poly(3-hydroxybutyrate) (PHB) in Alcaligenes latus cells. First PHB was depolymerized by either methanolic or hydrolytic digestion into methyl 3-hydroxybutyrate (Me-3-HB) or crotonic acid (CA), respectively. The resulting analytes were then subjected to analysis by headspace SPME/GC with flame ionization detection (FID). The two depolymerization/SPME/GC-FID methods were optimized and applied to the analysis of PHB in bacterial biomass harvested from a fermentation process that uses A. latus. Results were compared with those obtained using GC-FID analysis of MeOH/CHCl(3) digested samples. Excellent agreement was found between the three methods but the two SPME-based methods were environmentally friendly and easier to perform.     

A filter method with a priori and a posteriori parameter choice for the regularization of Cauchy problems for biharmonic equations

Numerical Algorithms - In the present paper, we devote our effort to Cauchy boundary value problems for biharmonic equations. In general, the investigated problem is ill-posed. Therefore, we...     

Antioxidative and α-glucosidase inhibitory constituents of Polyscias guilfoylei: experimental and computational assessments

Molecular Diversity - Searching for bioactive agents from medicinal plants, eleven constituents were isolated from Polyscias guilfoylei stem for the first time, including a nucleoside uracil (1),...     

A New Lignan from the Leaves of Styrax annamensis

Chemistry of Natural Compounds - Phytochemical investigation of the ethyl acetate extract of Styrax annamensis leaves has led to the isolation and determination of a new lignan,...     

Improved Copper(I)–NHC Catalytic Efficiency on Huisgen Reaction by Addition of Aromatic Nitrogen Donors

A simple addition with a large impact : Addition of aromatic amines such as phenanthroline and 4‐DMAP (4‐dimethylaminopyridine) increases copper(I)‐catalyzed azide alkyne cycloaddition (CuAAC) catalytic activity of [CuCl(SIMes)] at a large range of temperatures in such a way that efficient catalysis can safely take place in hydro‐alcoholic solvents (see scheme).